Three-Dimensional Viewing Chapter 12 Three-Dimensional Viewing
Viewing Analogous to the photographing process Camera position Camera orientation
Viewing Pipeline
Viewing-Coordinate System Viewing -Coordinate System or View Reference Coordinate System
Viewing-Coordinate System View plane (or projection plane) Perpendicular to the viewing zv axis View-plane normal vector N Choose a world coordinate position to determine N GKS PHIGS Determined by a look-at point relative to the view reference point.
Viewing-Coordinate System
Viewing-Coordinate System xv zv
Viewing-Coordinate System View-up vector V This vector is used to establish the positive direction for the yv axis. It is difficult to determine the direction for V that is precisely perpendicular to N. V is adjusted so that it is projected into a plane that is perpendicular to the normal vector.
Viewing-Coordinate System View-plane distance Choose the position of the view plane along the zv axis. The view plane is always parallel to the xvyv plane. Right-handed viewing system The convention of PHIGS and OpenGL To obtain a series of views of a scene Fix the view reference point and change the direction of N. The normal vector N is the most often changed viewing parameter
Viewing-Coordinate System
Viewing-Coordinate System
Transformation from World to Viewing Coordinates
Transformation from World to Viewing Coordinates
Projection Projection plane (or view plane) Center of projection (or projection reference point) An arbitrary point in the three-dimensional space. Usually it is the view point. Projectors Lines from the center of projection through each point in an object. Parallel projection The center of projection is located at infinity. All the projectors are parallel
Projection Perspective projection The center of projection is located at a finite point in three space. A distant line is displayed smaller than a nearer line of the same length.
Perspective Projection
Perspective Projection In three-dimensional homogeneous-coordinate representation